One or more ultrasonic sensors may be mounted on an automotive vehicle, for example a hybrid electric vehicle (HEV), enabling a distance determination between the sensor and an external object. Such an ultrasonic sensor may consist of at least a piezoelectric disc and a membrane, configured to convert electrical energy into mechanical energy, and mechanical energy into electrical energy. More specifically, an oscillated voltage may be applied to the piezo disc such that the piezo disc and membrane vibrate and generate ultrasonic waves at a frequency based on the frequency of voltage oscillation. After the waves are emitted, sensors wait for echoes to come back from objects, and when the echoes interact with the sensor/membrane, the membrane is excited to vibrate. The piezo disc attached to the membrane converts the vibration to voltage, and based on the timeframe of sending and receiving the ultrasonic wave, a distance determination to an object may be inferred.
In a vehicle, ultrasonic sensors may be utilized for inferring distance between a vehicle and obstacles during either assisted, or fully automated parking, for example. However, there are a number of factors that may affect optimal operation of an ultrasonic sensor. Such factors may include temperature, humidity, target surface angle, and reflective surface roughness. Of these four variables, determining humidity in a vehicle may be complicated, particularly in a case where a vehicle may not include a dedicated humidity sensor. Furthermore, estimation of ambient humidity is important for a number of engine operating parameters, such as an amount of exhaust gas recirculation (EGR), spark timing, combustion air-fuel ratio, etc.
Various kinds of sensors may be used to estimate the ambient humidity. As one example, oxygen sensors, such as a Universal Exhaust Gas Oxygen (UEGO) sensor used for exhaust air-fuel ratio control, may be used for ambient humidity estimation under selected conditions. Such oxygen sensors can be located in an exhaust passage or an intake air passage. In one example, shown by Surnilla et al. in US 20140202426, an exhaust gas oxygen sensor coupled to an engine bank may be utilized to opportunistically determine ambient humidity during conditions when the bank is selectively deactivated, and while the other bank continues to combust. A variable voltage may be applied to the sensor, and a change in pumping current may be correlated with the ambient humidity.
However, the inventors herein have recognized potential issues with such a system. As one example, humidity measurements may be non-specific, where humidity is estimated either opportunistically when possible, or when desired. For example, conditions may not always be present for conducting a humidity measurement via an exhaust gas oxygen sensor. Still further, where an exhaust oxygen sensor is used for humidity sensing, frequent application of a variable voltage may result in sensor blackening, and eventual degradation. Thus, for accurate and timely humidity measurements, an ability to selectively utilize one method of humidity measurement over another may be desirable, and may improve vehicle operating conditions that take humidity into account.
The inventors herein have identified an approach by which the issue described above may be at least partially addressed. In one example, a method is provided, comprising indicating relative humidity from differences between pairs of reflected signals from a single ultrasonic sensor coupled to a vehicle, each of the reflected signals having substantially equivalent transit time from an object back to the ultrasonic sensor; indicating relative humidity from one or more sensors coupled to the vehicle other than the ultrasonic sensor; and selecting which relative humidity indication method to use in response to environmental or vehicle operating conditions.
As an example, exhaust gas constituents may be detected from a gas sensor coupled to an exhaust of an engine which propels the vehicle, and during non-fueled operation of the engine, relative humidity may be indicated from the gas sensor. Where either the ultrasonic sensor or the gas sensor is utilized to conduct a relative humidity estimation, the method may include updating a previous humidity indication with the selected humidity indication.
As another example, vehicle operating conditions may be adjusted responsive to the relative humidity indication. For example, the method may include propelling the vehicle at least in part by the engine, where the engine includes an intake manifold and an exhaust manifold, and where the engine operates by combustion of fuel provided to the engine; controlling an amount of exhaust gas recirculated to the intake manifold of the engine while the engine is operating; and wherein adjusting vehicle operating conditions responsive to indicating relative humidity includes one of at least an amount of the exhaust gas recirculation, and an amount by which ignition timing of spark provided to the fuel for combustion is retarded or advanced. In this way, a humidity determination may be conducted via a suitable sensor, for example either a gas sensor or an ultrasonic sensor. The humidity determination may be conducted under conditions when a humidity determination is requested, for example responsive to an indicated change in ambient temperature greater than an ambient temperature threshold, a change in ambient pressure greater than an ambient pressure threshold, a threshold time of engine operation exceeding an engine operation time threshold, and a distance of vehicle travel greater than a distance threshold. By conducting a humidity determination via a suitable sensor, and adjusting engine operation based on the humidity determination, vehicle operating conditions may be improved, where said vehicle operating conditions may be based, at least in part on, a determination of relative humidity.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.